Fermiology and Superconductivity of Topological Surface States in PdTe_{2}

We study the low-energy surface electronic structure of the transition-metal dichalcogenide superconductor PdTe_{2} by spin- and angle-resolved photoemission, scanning tunneling microscopy, and density-functional theory-based supercell calculations. Comparing PdTe_{2} with its sister compound PtSe_{2}, we demonstrate how enhanced interlayer hopping in the Te-based material drives a band inversion within the antibonding p-orbital manifold well above the Fermi level. We show how this mediates spin-polarized topological surface states which form rich multivalley Fermi surfaces with complex spin textures. Scanning tunneling spectroscopy reveals type-II superconductivity at the surface, and moreover shows no evidence for an unconventional component of its superconducting order parameter, despite the presence of topological surface states.

Genetic susceptibility to Hodgkin's disease and secondary neoplasias: FISH analysis reveals patients at high risk of developing secondary neoplasia

BACKGROUND

Cytotoxic drugs administered before high-dose therapy (HDT) represent a significant factor in the development of leukemic complications in patients with lymphoid malignancies. This retrospective study was used to detect evidence of abnormal therapy-related myelodysplasia/secondary acute myeloid leukaemia (tMDS/sAML) clones before HDT in a subset of patients who subsequently developed secondary neoplasia.

PATIENTS AND METHODS

230 patients with non-Hodgkin's lymphoma (NHL) underwent HDT comprising cyclophosphamide and total body irradiation (TBI) with autologous hematopoietic progenitor-cell support. Thirty-three patients have developed tMDS/sAML and 20 of these were screened for the presence of emerging therapy-related abnormalities before HDT. A further 24 patients without evidence of secondary neoplasia were screened using fluorescence in situ hybridisation (FISH).

RESULTS

Significant levels of abnormal cells were identified in 20/20 patients screened who have developed secondary neoplasia compared with only three of 24 patients in the HDT control group who have not. The latter three patients have since died.

CONCLUSIONS

The triple FISH assay was developed to detect loss of chromosomal material from 5q31, 7q22 and 13q14. It can potentially identify those patients at risk of alkylating agent-induced leukaemia before they proceed to HDT. Used in a prospective manner, the triple FISH assay could permit more informed clinical management.

The characterisation of the lymphoma cell line U937, using comparative genomic hybridisation and multi-plex FISH

The cell line U937, which has been used extensively for studies of myeloid differentiation, bears the t(10;11)(p13;q14) translocation which results in a fusion between the MLLT10 (myeloid/lymphoid or mixed-lineage leukemia [trithorax, Drosophila, homolog]; translocated to 10; alias AF10) gene and the Ap-3-like clathrin assembly protein, PICALM (Clathrin assembly lymphoid myeloid leukaemia). Apart from this translocation, very little is known about the other genetic alterations in this cell line that may represent significant events in disease progression. In this study, conventional G-banding, CGH and M-FISH have been used to characterise fully all of the cytogenetic alterations present in the U937 cell line. M-FISH analysis confirmed the presence of the t(10;11) and an apparently normal copy of both chromosomes 10 and 11. A t(1;5) translocation was observed as well as several unbalanced rearrangements. CGH detected amplifications resulting from duplications of 2q, 6p and 13q. These changes could result in fusion gene products involved in carcinogenesis or the positions of putative oncogenes and tumour suppressor genes. A good correlation between conventional G-banding, CGH and M-FISH was observed.

Localisation of a novel region of recurrent amplification in follicular lymphoma to an approximately 6.8 Mb region of 13q32-33

Follicular lymphoma (FL) is characterised by the presence of the t(14;18)(q32;q21) and represents approximately 25% of new cases of non-Hodgkin's lymphoma. While the t(14;18) is a well-documented rearrangement, the role of secondary cytogenetic abnormalities in the development and progression of these tumours remains unclear. Comparative genomic hybridisation was used to characterise changes in DNA copy number in tumour DNA from patients with this malignancy. The mean numbers of deletion and amplification events found in each of the 45 samples studied were 1.8 and 2.3, respectively. Regions of recurrent (>10% tumour samples) gain involved chromosomes 2p13-16 (16%), 7 (20%), 12 (16%), 13q21-33 (18%), 18 (27%), and X (36%) and frequent losses localised to 6q (29%) and 17p (20%). Amplification of chromosome 13 represents a novel finding in FL. The minimal amplified region was refined to a 6.8-Mb interval of 13q32-33 between the BAC clones 88K16 and 44H20 by fluorescence in situ hybridisation studies using metaphase chromosomes derived from tumour material. There are a number of reports in the literature suggesting that amplification of chromosome 13 also occurs in other human cancers. The location of the putative oncogene on 13q described here in follicular and transformed lymphoma may also be important in the evolution of many other malignancies.

Detection of chromosome abnormalities pre-high-dose treatment in patients developing therapy-related myelodysplasia and secondary acute myelogenous leukemia after treatment for non-Hodgkin's lymphoma

PURPOSE

To assess whether pre-high-dose therapy (HDT)-related factors play a critical role in the development of therapy-related myelodysplasia (tMDS) or secondary acute myelogenous leukemia (sAML).

PATIENTS AND METHODS

Twenty-nine of 230 patients with a primary diagnosis of non-Hodgkin's lymphoma (NHL) developed tMDS/sAML after HDT comprising cyclophosphamide and total-body irradiation (TBI) supported by autologous hematopoietic progenitor cells. G-banding and fluorescence in-situ hybridization (FISH) were used to detect clonal cytogenetic abnormalities.

RESULTS

The majority of patients showed complex karyotypes at diagnosis of tMDS/sAML containing, in particular, complete or partial loss of chromosomes 5 and/or 7. Using single locus-specific FISH probes, significant levels of clonally abnormal cells were found before HDT in 20 of 20 tMDS/sAML patients screened, compared with three of 24 patients screened who currently have not developed tMDS/sAML, at a median follow-up of 5.9 years after HDT.

CONCLUSION

Prior cytotoxic therapy may play an important etiologic role and may predispose to the development of tMDS/sAML. Using a triple FISH assay designed to detect loss of chromosomal material from 5q31, 7q22, or 13q14, significant levels of abnormal cells can be detected before HDT and may predict which patients are at increased risk of developing secondary disease. Further prospective evaluation of this FISH assay is warranted to determine its predictive power in this setting.

The use of real-time quantitative polymerase chain reaction and comparative genomic hybridization to identify amplification of the REL gene in follicular lymphoma

Using comparative genomic hybridization (CGH), aberrations in DNA copy number were studied before and after transformation of follicular lymphoma to diffuse large B-cell lymphoma in six patients (15 lymph node biopsies in total). The most common and also the most discrete and intense amplification occurring in four out of 15 biopsies from three different patients was of 2p13-16. Using real-time quantitative polymerase chain reaction (RQ-PCR), REL amplification was found to be implicated at this locus. This technique also identified amplified REL in a further two biopsies, presumably below the detection level of CGH. REL amplification was quantified by comparing it, in most cases, with three endogenous reference genes, albumin, beta2-microglobulin and CD8alpha, that lie close to REL on 2p. There was no correlation apparent between 2p13-16 amplification or REL amplification and transformation. This study shows the usefulness of coupling CGH, for detecting recurring abnormalities, with the real-time PCR technique for rapid gene dosage quantification and confirms that the REL gene is a potential candidate in the pathogenesis of a particular subset of follicular lymphomas.